The present invention concerns a process for the production of dual-functional ion exchange resins from lignocellulosic agricultural material involving anionization of the lignocellulosic agricultural material with citric acid and then cationization of the lignocellulosic agricultural material with dimethyloldihydroxyethylene urea (DMDHEU) and choline chloride, or cationization of the lignocellulosic agricultural material with DMDHEU and choline chloride and then anionization of the lignocellulosic agricultural material with citric acid.
Ion exchange resins are adsorbents that effectively remove anions or cations from various types of industrial and municipal wastewater, storm water, and residential drinking water. Contamination of these water sources by anionic and cationic environmental pollutants is a significant problem in many parts of the United States. Thus the demand for ion exchange resins in the United States is currently about 280 million pounds and is expected to increase at about 5% per year for the forseeable future. Ion exchange resins, which can be produced by graft polymerization of functional anionic or cationic groups onto a synthetic bead comprised of polymers of styrene and divinylbenzene or produced by chemical attachment of either anionic or cationic functional groups on a natural polymer such as cellulose, are most commonly used to remove toxic or potentially toxic metal ions such as cadmium, copper or lead and anions that contain arsenic, selenium or chromium.
Agricultural by-products as a whole exceed 700 billion pounds per crop year. Most of these by-products are considered to be low-value waste with little ion exchange activity. While various methodologies exist for the creation of anion or cation exchange properties on plant by-products and cellulosic fibers, there remains a need to create dual-functional ion exchange materials from agricultural by-products that are cost effective and simultaneously efficacious toward both anions and cations of environmental concern. The present invention relates to the development of specifically modified agricultural by-products that possess enhanced adsorption properties with respect to the uptake of both anions and cations.